infallible

Infallible, a.

Etymology: [Pref. in- not + fallible: cf. F. infallible.]

1. Not fallible; not capable of erring; entirely exempt from liability to mistake; unerring; inerrable. Dryden.

2. Not liable to fail, deceive, or disappoint; indubitable; sure; certain; as, infallible evidence; infallible success; an infallible remedy. To whom also he showed himself alive, after his passion, by many infallible proofs. Acts i. 3.

3. (R. C. Ch.)

Incapable of error in defining doctrines touching faith or morals. See Papal infallibility, under Infallibility.

Shades of meaning

Fernald has no entry of its own for infallible; he lists it under necessary.

Where he writes about it:

An infallible proof is one that necessarily leads the mind to a sound conclusion. — from necessary

Synonyms

necessary essential indispensable inevitable needed needful required requisite unavoidable undeniable

Antonyms

absurd casual contingent needless non-essential optional precarious unnecessary useless worthless

etymology Webster’s online